Toxoplasma gondii

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Toxoplasma Gondii

Scientific classification

Kingdom:	Protista
Phylum:	Apicomplexa
Class:	Conoidasida
Subclass:	Coccidiasina
Order:	Eucoccidiorida
Family:	Sarcocystidae
Genus:	Toxoplasma
Species:	T. gondii

Binomial name

'''Toxoplasma gondii'''
(Nicolle & Manceaux), 1908

Toxoplasma is a genus of parasitic protozoa whose definitive host is cats but which can be carried by the vast majority of warm-blooded animals, including humans. Toxoplasmosis, the disease it causes, is usually minor and self-limiting but can have serious or even fatal effects on a fetus whose mother first contracts the disease during pregnancy or on an immunocompromised human or cat. It belongs to the phylum Apicomplexa and Toxoplasma gondii is the only known member species of the genus Toxoplasma.

1 Life cycle
2 Toxoplasmosis
3 References in fiction
4 References
5 External links

[edit] Life cycle

The life cycle of Toxoplasma gondii has two phases. The sexual part of the life cycle takes place only in members of the Felidae family (domestic and wild cats), which makes these animals the parasite's primary host. The asexual part of the life cycle can take place in any warm-blooded animal, like other mammals (including felines) and birds.

T. gondii constructing daughter scaffolds within the mother cell.

In the intermediate non-Felidae hosts, the parasite invades cells, forming intracellular so-called parasitophorous vacuoles containing bradyzoites, the slowly replicating form of the parasite^[1]. Vacuoles form tissue cysts mainly within the muscles and brain. Since they are within cells, the host's immune system does not detect these cysts. Resistance to antibiotics varies, but the cysts are very difficult to eradicate entirely. Within these vacuoles T. gondii propagates by a series of binary fissions until the infected cell eventually bursts and tachyzoites are released. Tachyzoites are the motile, asexually reproducing form of the parasite. Unlike the bradyzoites, the free tachyzoites are usually efficiently cleared by the host's immune response, although some manage to infect cells and form bradyzoites, thus maintaining the infection.

Tissue cysts are ingested by a cat (e.g., by feeding on an infected mouse). The cysts survive passage through the stomach of the cat and the parasites infect epithelial cells of the small intestine where they undergo sexual reproduction and oocyst formation. Oocysts are shed with the feces. Animals and humans that ingest oocysts (e.g., by eating unwashed vegetables etc.) or tissue cysts in improperly cooked meat become infected. The parasite enters macrophages in the intestinal lining and is distributed via the blood stream throughout the body.

Acute stage toxoplasma infections can be asymptomatic, but often gives flu-like symptoms in the early acute stages, and like flu can become, in very rare cases, fatal. The acute stage fades in a few days to months, leading to the latent stage. Latent infection is normally asymptomatic; however, in the case of immunocompromised patients (such as those infected with HIV or transplant recipients on immunosuppressive therapy), toxoplasmosis can develop. The most notable manifestation of toxoplasmosis in immunocompromised patients is toxoplasmic encephalitis, which can be deadly. If infection with T. gondii occurs for the first time during pregnancy, the parasite can cross the placenta, possibly leading to hydrocephalus, intracranial calcification, and chorioretinitis, with the possibility of spontaneous abortion or intrauterine death.

[edit] Toxoplasmosis

Main article: Toxoplasmosis

Behavioral modifications of the host

It has been found that the parasite has the ability to change the behavior of rats and mice - making them less fearful of cats. This effect is advantageous to the parasite, which will be able to sexually reproduce if its host is eaten by a cat. ^[2] There has been speculation that human behaviour may also be affected in some ways, and correlations have been found between latent Toxoplasma infections and various characteristics such as increased risk taking behavior, slower reactions, feelings of insecurity, and neuroticism. ^[3]

Several independent pieces of evidence point towards a role of Toxoplasma infection in cases of schizophrenia and paranoia. ^[4]

Alteration of human sex proportion A recent study ^[5] has indicated Toxoplasmosis is also correlated strongly with an increase in boy births in humans. According to the researchers, depending on the antibody concentration, the probability of the birth of a boy can increase up to a value of 0.72 ... which means that for every 260 boys born, 100 girls are born. The study also notes a mean rate of 0.60 to 0.65 (as opposed to the normal 0.51) for Toxoplasma positive mothers.

How to prevent infection

See toxoplasmosis.

[edit] References in fiction

Parasite Pig by William Sleator with an alien version of Toxoplasma gondii
In the book and film Trainspotting, a character died from having Toxoplasmosis in addition to HIV.
Peeps by Scott Westerfeld, where characters are infected by behavior-modifying parasites.
In "Resident Evil 4" a journal of the character Luis Sera mentions "Toxoplasma gondii" in addition to other parasites known to change the behavior of the host.
In House - season 1 - episode 17, "Role Model", a US Senator is initially diagnosed with toxoplasmosis.
In the book "Not Married, Not Bothered: An ABC for Spinsters" by Carol Clewlow, the narrator Riley Gordon suggests that infection with the parasite makes women more attractive to men.
On 365Tomorrows, the story Red String looks at a personified toxoplasma gondii's influence on humanity's evolution

[edit] References

^ Dubey JP, Lindsay DS, Speer CA (1998). Structures of Toxoplasma gondii Tachyzoites, Bradyzoites, and Sporozoites and Biology and Development of Tissue Cysts. Clin Microbiol Rev, 11(2):267–299. full text
^ Berdoy M, Webster J, Macdonald D (2000). Fatal Attraction in Rats Infected with Toxoplasma gondii. Proceedings of the Royal Society of London, B267:1591-1594. CiteULike
^ Carl Zimmer, The Loom. A Nation of Neurotics? Blame the Puppet Masters?, 1 Aug. 2006
^ E. Fuller Torrey and Robert H. Yolken. Toxoplasma gondii and Schizophrenia, Emerging Infectious Diseases, November 2003. full text
^ Jaroslav Flegr. Women infected with parasite Toxoplasma have more sons, Naturwissenschaften, August 2006. full text